U.S. Pat. No. 5,517,313, the disclosure of which is incorporated herein by reference, describes a fluorescence sensing device comprising a layered array of a fluorescent indicator molecule-containing matrix (hereafter “fluorescent matrix”), a high-pass filter and a photodetector. In this device, a light source, preferably a light-emitting diode (“LED”), is located at least partially within the indicator material, such that incident light from the light source causes the indicator elements to fluoresce. The high-pass filter allows emitted light to reach the photodetector, while filtering out scattered incident light from the light source. An analyte is allowed to permeate the fluorescent matrix, changing the fluorescent properties of the indicator material in proportion to the amount of analyte present. The fluorescent emission is then detected and measured by the photodetector, thus providing a measure of the amount or concentration of analyte present within the environment of interest.
One advantageous application of a sensor device of the type disclosed in U.S. Pat. No. 5,517,313 is to implant the device in the body of an organism (e.g., a human or animal), either subcutaneously or intravenously or otherwise, to allow instantaneous measurements of analytes to be taken at any desired time. For example, it is desirable to measure the concentration of oxygen in the blood of patients under anesthesia, or of glucose in the blood of diabetic patients.
Variations and improvements on the sensing device described in U.S. Pat. No. 5,517,313 are described in U.S. Pat. Nos. 6,330,464 and 6,400,974, as well as in United States Patent Application Publication No. 2013/0211213, the respective disclosures of which are hereby incorporated by reference in their entireties.
Existing sensor systems, including sensors and systems described in the disclosures referenced above, comprise a ‘grain of rice’ sized sensor configured to be implanted in vivo subcutaneously and that includes all of the functional electronics needed to enable implantable sensing of glucose or other analyte of interest. These functional electronics include the sensing element(s), such as light sources(s) (e.g., LED), filter(s) and photosensor(s), the optical interface, the circuitry that generates signals having strength and/or other characteristics that are dependent on the strength and/or other detectable characteristics of the optical radiation detected by the sensing elements, the integrated circuit functionality to wirelessly communicate the signals and receive commands, and an antenna that is inductively coupled to an antenna of a reader/transmitter that is external to the organism in which the sensor is implanted. Such a sensor configuration is well-suited for insertion of the sensor element in an interstitial space and communication with a reader/transmitter that is worn outside the skin, but in close to proximity to the implanted sensor element.
This close proximity between the implanted sensor element and the external reader/transmitter does provide good telemetry coupling between the sensor element and the external reader/transmitter as well as access to glucose (or other analyte) concentration in the interstitial fluid.
A shortcoming that exists with the state of the art, however, is that the system as described above is dependent on having within the sensor element an antenna that can receive power and commands from an external reader/transmitter, as well as sensing the presence of analyte at the same location at which the sensor element is implanted. Such dual requirements sometimes conflict with each other and can limit the range of applications in which this sensor system can be used to detect analytes in vivo and wirelessly communicate with an external device.